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Genetic counseling: Advanced Maternal Age - Amniocentesis
Advanced Maternal Age - Amniocentesis Introduction *Welcome and acknowledge any prior phone contact. *Discuss the reason for referral. Do they understand why they were sent to genetics? *Assess their concerns and what they hope to gain from the session. *Assess their degree of knowledge about genetics, heredity, AMA, etc. *Provide overview of the session and discussion topics. Prenatal Intake *Obtain client and partner information (age, occupation, ethnicity, religion, consanguinity, health) *Elicit family history and construct pedigree. *Pregnancy history (dates, procedures, exposures, complications) *Discuss population pregnancy information - every pregnancy has a 3-5% risk for congenital malformations; every pregnancy has a 2-3% risk of miscarriage. What is AMA? *Advanced maternal age applies to anyone aged 35 years or above at the expected date of delivery. *As maternal age increases, the risk of birth defects (particularly chromosomal abnormalities) increases. *Age 35 is the cutoff for AMA because this is the point where the procedural risk equals the risk of aneuploidy. What are chromosomal abnormalities? *Explanation of chromosomes. *Explanation of meiosis, haploid germ cells, fertilization to a diploid zygote. *Explanation of non-disjunction. Focus on how women are born with all their eggs and they mature with age. *Discuss common trisomies/monosomies (13, 18, 21, 47XXY, 45X), show karotypes, and give general description of clinical features and prognoses. Risk Assessment *Discuss client's age-related mid-trimester risks for any chromosomal abnormalities and for Down syndrome in particular. *Record data on intake. What are the testing options? *Triple Marker Screening: **Maternal blood test performed at 15-22 weeks. **Screening test only, NOT diagnostic. **Indirect measurement of fetal AFP, hCG, uE3 production. **Detects approx. 85% NTDs, up to 85-90% of DS, and up to 80% of Trisomy 18 in women with AMA. **False-positive rate of 25% in women over 35 years of age. **Does not detect all chromosomal abnormalities assoc. with AMA Ultrasound *Can detect many major birth defects. *Some fetuses with chromosomal abnormalities have characteristics that can be seen by ultrasound as "markers", but others have no visible anomalies. *Ultrasound can NOT diagnose chromosome abnormalities. Amniocentesis *Medical procedure that removes a small sample of amniotic fluid (made of fetal urine, contains fetal skin cells) from the amniotic sac surrounding the fetus. *Usually performed between 15-18 weeks (although some labs will interpret data from 13.5 to 21 weeks) *Fluid is used for genetic analysis - fetal karyotyping, biochemical studies, DNA studies, alpha-fetoprotein and acetyl cholinesterase measurements. Amnio Procedure *Procedure takes 20-45 minutes (1-2 minutes for needle insertion). *May be required to have a full bladder. *Lie down on back with hands folded behind your head. *Abdomen cleansed with betadeine. *Local anesthetic (xylocaine) may be used to numb the outer layer of skin - this may feel like a pin prick followed by a stinging or burning sensation. *Ultrasound is used to locate the fetus and placenta, identify the pocket of fluid, and guide the needle. *Physician inserts the needle (22 gauge with a stylet) through the abdomen and into the uterus - some discomfort may be felt when the needle enters the skin and then the uterus (may feel like a menstrual cramp); a sharp pain lasting a few seconds may be felt when the needle enters the amniotic sac. *Stylet is removed and the first few cc of fluid are discarded due to possible maternal cell contamination. About 20 cc (1 tablespoon) of amniotic fluid is removed - may feel pressure in the lower abdomen when the fluid is withdrawn; is quickly replaced by the fetus. *Needle is removed, bandage applied, fetal heart activity is monitored by ultrasound, no overnight hospital stay. *Fluid is sent to lab and results are available in 1-2 weeks. Discuss how results will be received. *About 95% of women receive a negative result. *Total cost is $600-$900. *Afterwards, no strenuous activity for 24 hours. Follow up with MSAFP at 16-18 weeks and ultrasound at 18-20 weeks. Benefits of Amnio *Accuracy of karyotype is >99% (NTD detection is about 90-96%). *Can detect chromosomal abnormalities (aneuploidies). *Can detect neural tube defects (spina bifida, anencephaly). *Tells the sex of the fetus. Limitations of Amnio *Does not detect all possible birth defects (only about 10% of 400 known congenital malformations). *Cannot predict the severity of the defect/disorder. *If first procedure fails, a second may be attempted that same day. If it doesn't work, then additional procedures should be postponed for 3-7 days. *Cell culture failure could occur (rare, <1%). Risks Associated with Amnio *Risk of miscarriage - 1/200 (0.5% beyond background risk). *Rh (-) mothers must be given RhoGam in order to prevent blood group sensitization. *Uterine cramping is not uncommon. *Notify your doctor is you have transient spotting or leakage of amniotic fluid (2-3% of cases). *Very rare chance of infection to uterus, hemorrhage, or maternal death. *Risk of birth defects due to amnio is remote (risk of clubfoot increased during early amnio). Conclusion *Discuss psychosocial issues that may arise. *Remind that no decision has to be made today. *Review and summarize. *Answer final questions and concerns. *Give out patient resources. Notes The information in this outline was last updated in 2001. Material obtained under GFDL Licence from http://en.wikibooks.org/wiki/Handbook_of_Genetic_Counseling